Radio shield for spark plugs



23, 1937. RABEZZANA ET AL 2,071,572

RADI O SHIELD FOR SPARK PLUGS Filed Dec. 50, 1935 Patented Feb. 23, 1937UNITED STATES RADIO SHIELD ron SPARK PLUGS Hector Rabezzana andAlexander J. Battey, Flint,

Mich assignors to General Motors Corporation, Detroit, Mich., acorporation of Delaware Application December 30, 1935, Serial No. 56,646

6 Claims.

Our invention relates to shielded spark plugs for preventing hightension currents used for.

igniting the combustible mixture supplied to internal combustionengines, from interfering with the operation of radio sending andreceiving and analogous sensitive apparatus located adjacent the engine;and the object thereof is to provide shielding means which, whileeffective for shielding purposes, is so designed and arranged that itwill reduce the flow of heat from ,the metallic base of the spark plug,which is in good heat conducting relation to the cylinder of the engine,to the cable whereby current is supplied to the plug to a lesser amountof heat flow than has heretofore commonly been the case. The drawingaccompanying and forming a part of this specification illustrates thepreferred form of our invention; and the particular features wherein thesame consists, and which distinguish it from prior shielded spark plugs,arepointed out in the concluding claims.

In the drawing:

Figure 1 is a sectional view upon a central plane extendinglongitudinally thereof, showing a shielded spark plug made in accordancewith our invention.

Figure 2 is a view showing a section upon a transverse plane indicatedby the line 2-2, Figure 1.

Referring to the drawing, the numeral 6 designates a hollowmetallic-base member made, ordinarily, from cold rolled steel barmaterial, and which base has a lower externally threaded part which isthreaded externally, as shown, to screw into a threaded spark plugopening in an internal combustion engine cylinder; and which basesupports the grounded or shell electrode 1 of the plug. This base ishollow and annular in form, and within the-same and supported therefromis the central insulated electrode 8 of the plug, the inner end of thelatter being arranged adjacent the shell electrode 1 to provide a sparkgap at 9. The central electrode may be insulated from the shell or base6 in any way but asshown said electrode is surrounded by a mica tube orcigarette I0 extending longitudinally thereof, the ends of said tubebeing in turn surrounded by stacks II, 12 of mica washers, this being anarrangement of insulation common in mica insulated spark plugs. Theelectrode 8 has an enlarged head I3 at its lower end, and a metalliccollar or terminal I at its upper end, which members abut against thewashers H, I2 and secure the central electrode and the insulationtherefor together.

The central electrode with the insulation therefor may be permanentlyassembled with the metallic shell 6 but in the preferred form of ourinvention illustrated said parts are carried by a tubular externallythreaded nut l5 which screws into an internally threaded passage l6 atthe upper end of the hollow shell; so that the central electrode, theinsulation therefor and the supporting nut l5 comprise a single unitarystructure which is removable in its entirety from, and replaceablewithin the interior of the support or shell 6; to which end said nut hasa hexagonal portion I! as shown.

The metallic base 6 has a cage portion shown as comprising threecircumferentially spaced bars l8 extending upwardly therefrom and beyondthe outer insulating member II and terminal l4, and the upper endsofwhich bars are connected together by an internally threaded ring memberIS; the base, the bars and the ring member being preferably madeintegral with one another.

Surrounding the outer insulating member II and extending beyond thesame, and beyond the outer end of the cage bars l8 and the ring I9, is atubular insulating member 20 made of porcelain, bakelite, or equivalentinsulating material; said member being shown as supported by an annularledge 2! provided by making the mica washers l I next to the tubular nutl5 larger than those next to the terminal M, as shown; a resilientwasher 22 being interposed between the ledge 2| and an annular shoulderwithin and adjacent the lower end of the insulating member, as shown.The lower portion of said insulating member 20 surrounds the upper endof the upper insulating member I l, and said member is shown as providedwith an internal annular seat portion or surface at 23 which fitsclosely around the terminal M. The upper part 24 of said insulatingmember is tubular in form to receive a depending terminal 25, made ofinsulating material, of a supply cable connecter indicated by thenumeral 26 whereby current is supplied to the central electrode 8; saiddepending part having a conducting rod 21 the lower end of which carriesa spring 28 which contacts with the central electrode terminal It totherebyprovide an electrical connection between a supply cable and thecentral insulated electrode of the-spark plug. The rod 21 is threaded at29 and screws into a passage provided for it in the depending part 25 ofthe cable connecter as shown.

The numeral 30 designates a thin metallic sheath tubular in form andwhich sheath surupper end of which is inturned to provide a flange 3|which overlies the upper end of said insulating member; a yieldablewasher 32 being interposed between said flangeiand upper end. The lowerend of the. sheath is preferably turned inward beneath the lower end ofthe insulating member 20, as shown at 33, so that the sheath andinsulating member when thus assembled to- ,gether form a unitarystructure. The sheath 30 while in virtual contact with-the exteriorsurface of the insulating member 20 fits somewhat loosely about the sameso that it may move freely along said member as the washer 32 iscompressed during the assembling of the parts.

The numeral 34 designates an externally threaded tubular coupling sleeveor connecting member which screws into the internally threaded ring l9,said member having an inturned flange 35 at its upper end which overliesan outwardly extending flange 36 of the usual metallic casing of thesupply cable connecter 26, to thereby secure the connecter to the sparkplug or, more strictly, to the ring l9 which connects the outer ends ofthe cage bars I8. Said flange 36 is clamped between the inturned flange35 and the inturned flange 3| as the coupling member 34 is screwed intothe ring I5; and the metallic sheath 36 is free to move downwardrelative to the insulating member 20 as the washer 32 yields during theassembling of the parts; downward movement of the insulating memberitself being prevented by the ledge 2|as will be appreciated.

' After the coupling member or sleeve 34 has been screwed into the ringl9 sufliciently to secure the tubular nut I5 proper tightness betweenthe inturned flange 35, the outwardly extending flange 36, and theinturned flange 3| and washer 32 and the upper end of the insulatingmember 20, said coupling member is secured in place by a lock nut 31which engages the upper side of the ring l9 as will be understood. Thecoupling member 34 is provided with holes 38 adjacent its upper end tohelp impede the flow of heat to the cable connecter 26 and to permitsaid member to be grasped by the fingers in screwing said member intothe ring l3; and the peripheryof said member as well also as of the locknut 31 are shown as knurled to facilitate the securing of the cableconnecter 26 to the spark plug, and the removal of said connecter fromthe spark plug. The cable connecter 26 may be disassembled from the plugby unscrewing the coupling sleeve 34, whereupon the sheath 30 be removedthrough the ring l9; and the central electrode with its insulatingmembers may likewise be removed through the ring by unscrewing from thebase 6. 3

The cable connecter 26 has an outer metallic casing, as explained, andtightening of the sleeve member 34 presses the parts 35, 36, and 3| intofirm contact with one another; so that the act of securing the connecterto the spark plug grounds both the metallic casing thereof and themetallic sheath 30 upon the metallic base 6 of the plug. Substantiallythe same grounding action, however, will be secured if the inturnedflange 3| is not present, as there will always be a sufficiently goodcontact between the sheath 30 and the interior of the coupling member 34to effectively ground the sheath upon the base 6 of the plug.

In our improved spark plug electrical shielding so far as the plug perse is concerned (that is which bars are connected together by an annularand insulating member-20 may not taking into account the usual metallicshield of the supply cable and the metallic casing of the connecter 26,which are grounded upon the base of the plug as hereinbefore explained)is due to the grounded metallic sheath 36, which :may terminate as closeas desired to the tubular nut l5 (or to the upper end of the shell orcasing 6 if the central electrode and its insulation are. permanentlyassembled with the shell), thus reducing the length of high tension leadrepresented by a short section of the central electrode which is notshielded to as short a length as may be desired; and the bars l8 will infact form a shield for even the short length of central electrodebetween the lower end of the sheath 3!! and the nut l5, or the upper endof the shell of the plug.

The cage bars l8 being few in number, and comparatively long and ofcross-sections not necessarily greater than is necessary for adequatemechanical strength, it follows that the flow of heat to the cableconnecter casing 26 and to the usual rubber insulation of the supplycable through the bars will be reduced to a negligible amount; and thewall of the metallic sheath 36, being extremely thin, acts likewise tominimize the flow of heat to the casing 26 and to the supply cable.

vention, we claim and desire to secure by Letters Patent: V

1. In a shielded spark plug, a hollow metallic base member having anexternally threaded part adapted to screw into an opening in an enginecylinder; a central electrode and an insulating member therefor, saidelectrode and insulating member being supported by said base member;circumferentially spaced bars extending upward from the base member, andthe upper ends of ring member; a tubular insulating member surroundingthe insulating member for said central electrode, and which insulatingmember extends beyond said ring member; a tubular metallic shieldsurrounding said last mentioned insulating member, and which shield iselectrically connected with said metallic base member so as to begrounded thereupon; and means for connecting the metallic casing of asupply cable connecter with said ring member, said connecting meansacting also to ground said casing upon said base member.

2. In a shielded spark plug, a hollow metallic base member having anexternally threaded part adapted to screw into an opening in an enginecylinder; a central electrode and an insulating member therefor, saidelectrode and insulating member being supported by said base member;circumferentially spaced bars extending upward from said base member andbeyond the upper ends of said central electrode and insulating member,and the upper ends of which bars are connected together by a threadedring; a tubular insulating member supported by the insulatinl member forsaid central electrode and extending beyond the upper end thereof andbeyond said threaded ring; a tubular metallic shield surrounding saidlast named insulating member and extending throughout the lengththereof; and threaded means for connecting the metallic can ing of asupply cable connecter to said threaded ring, said connecting meansacting to groundl both said casing and said shield upon said metallicbase member.

3. In a shielded spark plug, a hollow metallic base member having anexternally threaded part adapted to screw into an opening in an enginecylinder; a central electrode and an insulating member therefor, saidelectrode and insulating member being supported within said base andsaid insulating member having an annular supporting ledge;circumferentially spaced bars extending upward from said base member andbeyond the upper ends of said central electrode and insulating member,and the upper ends of which bars are connected together by an internallythreaded ring; a tubular-insulating member having an internal annularshoulder adjacent its lower end which overlies the ledge aforesaid,

and which insulating member surrounds said first named insulating memberand extends beyond the upper end thereof and through-and beyond saidinternally threaded ring; a tubular metal shield surrounding said lastnamed insulating member and extending throughout the length thereof, andhaving an intumed flange at its upper end which ove lies the upper endof said insulating member; and an externally threaded sleeve engagingsaid internally threaded ring and having an inturned flange at its upperend for engaging a flange of a metallic casing of a supply cableconnecter, and for forcing said last named flange against the inturnedflange aforesaid at the upper end of said tubular metallic shield.

4. In a shielded spark plug, a hollow metallic base member having anexternally threaded part adapted to screw into an opening in an enginecylinder and an internally threaded passage at its upper end; a tubularexternally threaded nut within said internally threaded passage andremovable therefromf a central electrode and insulating-means -therefor,said electrode and insulating means being supported by said tubular nut;circumferentially spaced bars extending upward from said basemember andbeyond the upper ends of said central electrode and the insulating meanstherefor, and the upper ends of which bars are connected together by athreaded ring member; a tubular insulating member surrounding saidcentral electrode and the upper end of the insulating means therefor,and which insulating member is supported by the insulating means forsaid electrode and extends beyond the same and through and beyond saidthreaded ring member; a tubular metallic shield surrounding said lastnamed insulating member and extending throughout the length thereof,said shield and insulating member being removable through said ringmember; and threaded means for connecting the metallic casing of asupply cable connecter to said threaded ring member, said connectingmeans acting to ground both said casing and said shield upon saidmetallic base member.

5. As an element of a shielded spark plug, a

tubular insulating member having a lower por-' tion adapted to surroundan insulating member of the central electrode of a spark plug, aninternal ledgeadjacent its lower end whereby said member may besupported by a shoulder upon said insulating member, and an upperportion adapted to surround a terminal whereby current is supplied tosaid central electrode; a metallic shield member surrounding saidinsulating member and extending throughout the length thereof and havingan inturned flange at its upper end which overlies the upper end'of saidinsulating member, said shield member being loose upon said insulatingmember and capable of slight movement longitudinally thereof and ayieldable washer arranged between said inturned flange and the upper'end of said insulating mem ber.

6. In a shielded spark plug, a hollow metallic base member having anexternally threaded part adapted to screw into an opening in an'enginecylinder, and an internally threaded passage at its upper end; a tubularexternally threaded nut within said internally threaded passage andremovable therefrom; a central electrode and insulating means therefor,said electrode and insulating means being supported by said tubular nut;circumferentially spaced bars extending upward from said base member andbeyond the upper ends of said central electrode and the insulating meanstherefor, and the upper ends of which bars are connected together by athreaded ring member; a tubular insulating member surrounding saidcentral electrode and the upper end of the insulating means therefor,and which insulating member extends beyond the insulating means forsaidelectrode and through and beyond said threaded ring member; a tubularmetallic shield surrounding said last named insulating member andextending throughout the length thereof, said shield and insulatingmember and said tubular nut and the central electrode and insulatingmeans therefor being removable through said ring member; and threadedmeans for connecting the metallic casing of a supply cable connecter tosaid threaded ring member, said connecting means acting to ground bothsaid casing and said shield upon said metallic base member.

HECTOR RABEZZANA. ALEXANDER J. BATTEY.

